The present invention is concerned with a test carrier for the determination of so-called coagulation parameters, i.e. for the analysis of blood with regard to the components influencing the coagulation process.
For the quantitative and qualitative analytical determination of components of body fluids, especially of blood, so-called carrier-bound tests have recently been increasingly used. In these, reagents are embedded in appropriate layers of a solid test carrier which is brought into contact with the sample. The reaction of sample and reagents leads to a detectable signal, especially to a colour change, which can be evaluated visually or with the help of an apparatus, usually by reflection photometry.
Test carriers are frequently constructed as test strips which consist essentially of a longitudinal carrier layer of synthetic resin material and test fields applied thereon. However, test carriers are also known in the form of quadratic or rectangular platelets.
U.S. Pat. No. 4,477,575 describes agents and processes for the separation of plasma or serum from whole blood and especially test carriers for the diagnostic determination of components of body fluids (so-called parameters) which make it possible to determine component materials of whole blood in a simple manner. According to this patent specification, the plasma can be separated from the erythrocytes by allowing the whole blood to run through a layer of glass fibres with fibre diameters of less than 2.5 .mu.m which hold back the erythrocytes. The blood is preferably applied to one end of a rectangular glass fibre fleece from which the plasma is transported by capillary forces into the other region of the device. After the plasma-obtaining procedure, this fleece part filled with plasma is pressed against a matrix (paper, absorbent films or the like) containing the necessary reagents in which matrix is carried out the detection reaction for the parameter to be detected via remission measurements.
This simple plasma obtaining and plasma transport system can be used for all important clinical-chemical parameters with the exception of parameters which are to be determined involving haemostasiological determination. It is known that, in principle, coagulation analyses are to be carried out in synthetic resin or glass vessels which are inactivated by a coating of silicone resin because untreated glass influences the coagulatability of blood and plasma. Thus, due to activation, glass shortens the Quick one-phase coagulation time of plasmas, the coagulation factors of which lie within the normal range. In the case of lower percentage plasmas, the Quick one-phase coagulation time is prolonged due to inactivation of coagulation factors. In particular, glass inactivates Factors V and IIa. Due to this inactivation and thus falsely prolonged coagulation times, the diagnostic usefulness is destroyed because the ratios of the individual coagulation factors are displaced. The Quick value, given as a percentage, includes, besides the fibrinogen concentration, the activity of Factors II, V, VII and X. A pool plasma from healthy donors is defined as 100% plasma and, by means of dilution with physiological saline, appropriate lower percentage plasmas are prepared. By means of this dilution series, a reference curve is produced on the basis of which are determined the Quick values for patients' plasmas.
However, the partial thromboplastin time (PTT) is also negatively influenced by inactivation of Factors XII and XI. The detection of antithrombin III and heparin is considerably disturbed due to inactivation of thrombin by glass.